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Fish
The fish are the class of chordates that live completely in water. Their bodies have three main parts; the head, the trunk of the body and the tail. Their bodies are covered in scales and also a protective slime. They are important as a food source for animals.
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System
Type
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Fish
System
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| Digestion | A fish eats algae and plants and/or animals. Those that eat animals have teeth. |
| Muscular/Skeletal | A fish has an inner skeleton. It has two sets of fins, the pectoral fins that are near the head and the pelvic fins that are further down the body. Along the top of the trunk are the dorsal fins and fins towards the back or rear of the fish called anal fins. The dorsal and anal fins are for balance and the others for movement. |
| Nervous | A fish has a brain and a nervous system. Its eyes are positioned on either side of its body and are quite large, with no eyelid. Their retinas have both rods and cones. They have large pupils that let in a great deal of light. They have an inner ear but no outer ear opening. Since their bodies are the same consistency as water. Sound in water travels four times as fast as in the air. The fish also has a lateral line system just under the skin of its head and the top of its body that helps it detect motion and therefore prey. Fish have a nasal sac that helps them smell. Some fish produce a low voltage electrical current that keeps prey away. |
| Circulation | A fish is cold blooded. It has a heart, blood and blood vessels. |
| Respiration | A fish breathes through gills located on either side of the head. The gills are made up of tiny threadlike filaments. When the fish opens its mouth, water rushes in and the oxygen is pulled out through the blood vessels in these filaments. They also have an air bladder that allows them to rise or sink as it inflates or deflates. |
| Reproduction | A fish reproduces sexually. The female lays eggs outside her body and then a male comes along and sprays a liquid called milt which has many sperm cells. The eggs are then fertilized. The eggs contain yolk that feeds the young fish in the egg and some stays on to feed the fish after it hatches. A few fish carry their eggs in their bodies until birth. |
| Excretion | A fish gets rid of wastes through its anus. |
| Symmetry | A fish has bilateral symmetry. |
| Appearance | A fish is usually darker colored on top and lighter on the bottom to protect it from enemies. It is streamlined so that it can move through water rapidly. Fish can change their color rapidly with color and reflective cells in their skin pigmentation.Fish can range in size from less than an inch to sixteen feet. |
